Chlorofluorocarbons (CFCs) or Flons have in recent years been widely used as a coolant and cleaning agent. Since, however, it was revealed that they destroy the earth's ozone layer and contribute to global warming, it was decided in the Montreal Agreement that the use of CFCs should be eliminated throughout the world by the end of 1995. In order to meet this goal, various nations around the world are now actively collecting the remaining CFC gas reserves.
In dry etching using a reactive gas such as trifluoromethane (CHF.sub.3) or dichlorodifluoromethane (CCl.sub.2 F.sub.2), some portion of the reaction gas remains non-reacted and is discharged from the etching chamber. It is necessary therefore to provide a unit for processing such residual non-reacted halogenated hydrocarbon gas after the etching chamber of every dry etching machine in order to prevent the harmful gas from being released in the air.
Several methods have been proposed to change the collected CFCs to harmless substances which do not destroy the ozone layer. A typical conventional method is to decompose CFCs by heating them at high temperature, which of course requires a lot of energy. Another drawback is that decomposed CFCs generate various gases containing carbon, fluorine and chlorine which may be also harmful by themselves and require further processing to make them completely harmless.
Another method is proposed in the Publication No. H3-111065 of Unexamined Japanese Patent Application, in which ultraviolet ray of a certain wavelength is irradiated on CFCs to decompose them into CF.sub.2, C.sub.2 F.sub.4, and other fragments. This method has a similar drawback as above because the products CF.sub.2, C.sub.2 F.sub.4, etc. need further processing.
Conventional halogenated hydrocarbon processing systems provided to dry etching machines use an absorbent for absorbing the residual non-reacted halogenated hydrocarbon. The fixation of halogenated hydrocarbons by the conventional processing unit is, however, not complete and may cause desorption of the halogenated hydrocarbons from the absorbent unless the absorbent is properly treated.
In summary, there has been no effective method of completely making chlorofluorocarbons and halogenated hydrocarbons harmless.